Fig. 2. Axis induction by the MGO. (A) The scheme of tissue transplantation: a tissue fragment dissected from the anterior end of the primitive streak (Region V, VI; Fig. 5C) of mid-streak (MS) stage embryo is transplanted to the lateral region of the late-streak/no bud (LS/0B) stage host embryo. (B) After 24 hours of in vitro development, the host embryo contains an elongated structure (white arrowheads) of EGFP-expressing graft-derived tissues on its left flank. Sox2 activity, which is expressed in the neural tube of the host embryo, is also expressed in the ectoderm overlying the graft-derived tissue (black arrowheads, one out of two embryos containing grafts showed Sox2 induction). (C) EGFP-expressing graft tissue (white arrowhead) located at hindbrain level has induced Otx2 expression (black arrowhead, six of seven embryos containing grafts showed Otx2 induction) which is normally expressed in the fore- and midbrain regions. hf, head folds; nt, neural tube; som, somites. Scale bar: 200 µm.